Method of making an alloy



Jan.14,"1941., V L.SIMONS, 2,228,916-

f METHOD OF MAKING AN ALLOY Filed May 10', 1957 Sheets-sheaf. 1

Bean 8111110 1 I BY #Pfikt ATTORNEYS.

Jan. 14, 194.1. slums 2,228,916 METHOD OF MAKING ANALLOY Filed llay 10.1957 2 Sheets-Sheet 2 IN ENTORQ A5201: 514110118 ATTORN EYE PatentedJan. 14, 1941 UNITED STATES PATENT OFFICE 2,228,916 Mar-non or MAKING AN11.1.01:

Leon Simona, New York, N. Y. ApplicationMay 10, 1937, Serial No. 141,618

material. The invention also relates to an improved hard and refractorymaterial.

5 One of the objects of my invention is to make bodies of material whichinclude tungsten-carhide, and other compounds or elements which havehigh melting points.

Another object of my invention is to make an improved material of thetype which includes tungsten carbide or other ingredient which has ahigh melting point, and which also includes an additional metal having alower melting point than said tungsten carbide. This additional metalmay be cobalt or nickel or other metal, or alloy having a melting pointwhich is lower than the ingredient which has the high'melting point. Theingredient which has the high melting point preferably comprises atleast 50% by weight of Q the improved material, although the ingredientwhich has the lower melting point, such as cobalt or nickel, may bepresent in any desired proportion.

Another object of my invention is to provide :5 a material having ahigher proportion of nickel or cobalt or the like, than has hithertobeen practical.

, Another object of my invention is to provide an improved method ofmaking an alloy which 0 includes tungsten or tantalum orother metalhaving a high melting point.

Another object of my invention is to provide an improved hard alloywhich includes tungsten carbide or tantalum carbide or other carbides 5which have high melting points.

The finished product which is made according to my invention mayconsist'of minute particles of tungsten carbide or other carbides, whichhave beenmelted while in contact withcobalt or nickel to or othermaterial having a lower melting point than the carbide, and which hasbeen recrystallized from said melt. This application is in part acontinuation of application Serial No. 35,039, filed in the UnitedStates Patent Ofllce on Aui5 gust 7, 1935, now'Patent No. 2,151,874,dated Mar.

Alloys or cemented carbides of the type which I desire to improve, aredescribed in Schroter U. S. Reissue Patent No. 17,624 and in numerous 50other patents such as U. 5. Patent No. 1,805,364, U. S. Patent No.1,895,354, U. 8. Patent No. 1,892,653, U. S. Patent No.1,937,185, U. 8.Patent No, 1,950,356, French Patent No. 573,624, and others. 55 Theinvention relates to the improvement of 50mm. (ours-137) Myinvention'rel'ates to a new and improved" method of making bodies ofhardand refractory alloys or cemented carbides of any of the said types,or containing any of the ingredients specified in said patents, and italso generally applies to the manufacture of any type of alloy.

Other objects of my invention will be set forth 5 in the followingdescription and drawings which illustrate a preferred embodimentthereof, it being understood that the above statement of the objects ofmy invention is intended generally to explain the same without limitingit in any manner.

Fig. 1 shows the first step in the improved method. i

Fig. 2 diagrammatically shows apparatus which can be used for carryingout the second step'l5 of my method.

Fig. 3 is a detail sectional view, partially in elevation, showing howthe particles of tungsten carbide or the like can be enclosed in a metalshell which is closed at one end and which is open at the other end, inusing the apparatus which is shown in Fig. 2.

Fig. 4 shows another method of impinging the. particles-of tungstencarbide or the like against a mass of nickel or metal.

Fig. 5 is a microphotograph, made under a magnification of 1500, showingmaterial which has been fused and allowed to cool, according to themethodspecified herein, without the use of pressure.

Fig. 6 is a microphotograph, at the magnification above stated, showingthe improved material made according to the best embodiment of theinvention, and with the use of heat and pressure.

Fig. 7 is a microphotograph made at the magnification above stated andshowing the starting material which is used for making the improvedmaterial;

Heretofore, in making alloys of the old type which consisted of minuteparticles of tungsten carbide, said particles were cemented togetherwith cobalt or nickel, according to the old process, which was asintering process. In such old sintering process, the proportion ofnickel or cobalt did not exceed about 18% to 20% by weight of thetungsten carbide. The sintering process was not practical, with lessthan about 5% by weight of the nickel or cobalt, because the use of alower percentage resulted in a product which had voids,

According to my invention, thettungsten carbide or equivalent materialis preferably reduced to a particle size which is much finer than theparticle size which has heretofore been employed,

cobalt or other auxiliary 25 when a sintering mixture was madeaccordingto the prior art.

The usual practice has been to makesuch particles sufllciently fine topass through a No. 320 6 screen. A screen which is designated as No. 320has 320 holes per linear inch and these holes are substantially equallyspaced. Hence the particle size, accordingto the old method was about.0015 inch, (fifteen ten-thousandths of an inch).

10 According to my invention 1 reduce the tungsten carbide or the likemuch more finelyso that the particles are as fine as 0.0002 inch (twotenthonsandths of an inch). While I do not wish to be limited to suchvery fine particle size, this will serve as a practical working figure.The

4 particles may be even finer.

I then coat these fine partitcles of tungsten carbide or the like,intimately and sufiiciently with the cobalt or nickel or additionalmetal or material. By using very fine particles, having large surfaceareas in proportion to their volumes, I can coat the fine particles withsufiicient additional metal. For this purpose and in order to lower costof manufacture and to secure a sufficient and even coating, I prefer toproject the particles of tungsten carbide with sufflcient velocityagainst a mass or body of nickel or cobalt or the like. For thispurpose, and as shown in Fig. 1, the particles of tungsten carbide canbe projected by means of air pressure or other fiuid pressure, throughatube I, and the.

particles are projected at high velocity against a body 2, which is madeof nickel or cobalt or thelike. Said body 2 may be held horizontally orvertically or in any position.

The air. pressure which is utilized for projecting the particles oftungsten carbide may be derived from a source of compressed air whosepressure is as high as one hundred pounds -per square inch or evenhigher.

I do not wish to be limited to any particular velocity of the projectedtungsten carbide particles, and said velocity may be ashigh as isdesired.

As shown in Fig. 1, the particles of tungsten carbide may glance oif thestationary mass of nickel or cobalt and such particles are coatedsufficiently with nickel or cobalt or the like,

which is removed by impact or abrasion from the solid mass of nickel orcobalt. Some of the particles of tungsten carbide may be imbedded in themass of nickel or cobalt or the like. and such particles can be readilyremoved from the mass of nickel or cobalt or thelike, by meansoi' ascraping action, which, will finely divide the nickel or cobalt orthelike. 1

Likewise I can utilize apparatus of the general tyne which isexemplified in U. S. Patent 'No. 2,032.82? dated March 3, 1936, wherebythe "art cles 'of tungsten carbide are projected at hi' h velocityagainst an annular member made of nickel or cobalt or the like.

In passingthrough said apparatus, the particles of tungsten carbiderepeatedly strike the 55-annular body of nickel or cobalt, and the particles oftungsten carbide are repeatedly defiected from the annularmembermade of nickel or cobalt.

This operation continued in one or more,

70 stages until the particles of tungsten carbide have taken up therequired percentage. orpercentages I of' additional metal or material.If a tungsten carbide alloy is to be made, the per centageof nickelor'cobalt which is taken up 75 may be as low as five per cent or eventwo per cent, and as high as twenty-five percent or even higher.

I generally include within the invention alloys of the type abovementioned, containing tungsten carbide or other refractory material orrefractory carbide, and having more than eighteen percent of anadditional metal having a lower melting point than the tungsten carbideor the like.

I include generally any step in the manufacture of any alloy wherebyparticles of metal or alloy, of any size, are caused to impact withcoating-metal material. For example, projected particles of tungstencarbide and of nickel can be caused to collide with each other, whilesaid particles are moving at high velocity. This is to be distinguishedfrom the operation of a ball mill or the like in which the particles oftungsten carbide and nickel are merely rubbed against each other butwithout any impact or abrasive action.

As shown in Fig. 4, the particles P can be projected at a high velocityfrom the tube T, against the wall of a recess n of the large stationarymass N, which may be made of nickel or cobalt sten carbide or the likeare moved in the path shown, so as to rub off suflicient nickel orcobalt or the like, which clings to said fine particles.

After the fine particles of tungsten carbide or the like have beensufliciently coated with the coating metal, I can use any suitableprocess to form a coherent mass from said particles.

However, I prefer to use the process.and apparatus illustrated in Fig.2, although the improved process can be used with any type of apparatus.

Fig. 2 shows, a base I made of steel or other metal. The upper surfaceof the base I is provided with a covering member A which is made ofasbestos or of other material which is extremely refractory and whichhas high heatlnsulating properties. Member A is preferably rigid and itmay be made of the material known to the trade as "rock asbestos.

The upper surface member A is provided with l a recess, in which afilling '3 is located. Said filling 3 is also made of refractory andheat-insulating material. Said filling 3 -may consist of a mixture oflamp black and of silica.

The filling 3 isin the form of a dense and coherent block which has beenmadeby subjecting -a mixture of lamp black and silica to suitable whichis made of suitable refractory material.

Casing 2 can be made of quartz or of fused-alumina material of thetype-which is known as "alund I 4 7 Above the top surface of the blockA, casing 12 can be filled with material 9 in finelydiyided powder form-Said material 9 can have the same composition as the filling material 3so that filling material 9 has maximum heat-insulating properties.

While the material 9 is subjected to pressure during the operationof thedevice, said material 9 remains substantially in loose and powderedform.

it has a dense coherent filling 3' which is'iden tical with the filling3 of the block A.

A graphite mould 4 is provided with a bottom. planar surface which restson top of the. block a 3. The'block 3 projects outwardly beyond thebottom of. the mould.4, through a distance which is sumciently so as toprovide for eflicient heat insulation. This distance may be an eighth ofan inch or as much moreas is desired.

Suitable means are provided for preventing the mould 4 from shiftinglaterally relative to the block 3. For example, the adjacent surfaces ofthe block 3 and of the mould 4 can Be provided withinterfittingprojections and recesses. The interior of the graphite mould4 is filled with the coated tungsten carbide material or the like.Plunger 8 has a. cylindrical bottom portion .which fits slidably andvery closely in the cylindrical bore of the recessed upper portion 6 ofthe mould 4. The plunger 8 is also made of graphite and suitable meansare provided: for preventing any' lateral shift between plunger 8 andblock 3'. Said means can consist of suitable interfitting recesses andprojections. cal with the block 3 and it is located in the recess of amovable member A, which. is identical with the member'A. I

Block A is subjected to pressure by any suitable means such as removableweights i0. In compressing the material I, this being the coatedtungsten carbide or the like, I can vuse pressures as high as fourthousand'pounds per square inch. The material I is located in the fieldofthe hollow coil G which is supplied with a suitable high frequencycurrent. This high frequency current may have a frequency as high asseventy thousand cycles'per second and the cific temperatures ,a's thesemay depend upon the material which is being treated, the material I I isgenerally heated to a temperature between 2500 C. and 2600" C., if thematerial which is being treated is tungsten carbide, which has beencoated with about fiften per cent of nickel. However, the temperaturemay be lower and it may even be higher, depending upon the type ofmaterial which is being treated in the apparatus which is disclosed inFig. 2.

The coil G may be cooled by forcing water or other cooling mediumthrough the same, and for this purpose the coil G has an inlet end IIand an outlet end l2. 'Said coil G also has its ends provided withelectric couplings l4 and I5 to which theelectrical leads l4 and I5 areconnected. Said leads l4 and i5 are connected to a high frequencyconverter or any other sui After theapparatus has been assembled, sompressure, less than. the maximum working pressure, is applied to theplunger 8. This initial pressure may be about one-half of the maximumworking pressure, which maybe as high as4000 pounds per square inch. I

As soon as the initial pressure has been applied to plunger 8, currentis supplied to the coil G. The graphite mould 4 is preferably, but notnecessarily, of. the type which is sufflciently porous or absorbent soas to cause the driving out of the air or other gases which areintermixed with the material I, and some of the nickel or cobalt mayalso enter the wallof the recessed portion of the mould 4-. Indeed theworking The block 3' is identi- .induction.

The particles of the material. I therefore fuse from solid solution.

of the tungsten carbide material or the like to enter the material ofthe mould 4. For this purpose the mould .4 may be made of graphiteused-for making ultra fine filters." The wall of the recess of the mould4 may have a thickness of from one-quarter ofan inch to three-quartersof an inch,depending upon the'diameter of the recess.

While Fig. 2 is diagrammatic,

it is'substantially according to scale.

The high frequency 'current heats the material I by means of induction?'Iriorder to permit the properheating ofth'e'material 1, it may containand it preferably does contain a small percentage of ironwhich may be ashigh as two per cent. This iron or other paramagnetic material may beincorporated into the particles before they are coatedwith nickel orcobalt or the like. The iron or other auxiliary paramagnetic materialmay be omitted." j 1 It. is believed that the heating eifect is due inpart to conduction, in part'to the alternating magnetic polarity of theparticles, and in part by eddy currents, and also by' hysteresis. It isalso believed to be due in part to electrostatic so that the volume ofthe material 'I can be'diminished by the pressure. This additionalpressure is applied quite rapidly 'so that a slug of material is'formedfrom the material 1 andthe height of said slug is about twenty-five percent, less than the original height of the material.

The entire process should not take from more The close fit of plunger 8in the recess of 'the mould, causes the material 1 to be maintained in aspace which is substantially air-tight, during the heat and pressuretreatment. Likewise the material is treated quite rapidly so that anyoxidation of the tungsten carbide-or other oxidizable material issubstantially prevented, without us ing an inert or reducing atmosphere,although such atmosphere could be used.

While the material is being heated and subjeeted to pressure, the coil Gcan be continuously cooled so as to, maintain saidcoil at atemperatureof about 50* F. 7

After the current supply has been discontinued,

the cooling eilect of the coil G can be-continued. The coil G ispreferably spaced from the member 2,.whichis made of material which is.a good insulator against both heat :and electricity.

The above" directions are mainly for making a E slug which can be usedfor making a die for drawing wire.

The final material consists predominantly of tungsten carbide crystals(containing iron orthe like), if the starting material was coatedtungsten carbide. These tungsten carbide crystals are regular in shape,indicating recrystallization The matrix or cementing material betweenthe crystals is a solid solution of cobalt and tungsten carbide, if.cobalt has been used as the cementing material. p

5 In effect the particles 1 act as the secondary magnetic circuit of thealternating electro-magnetic flux.

It will be noted that the ends of the mass 1 are not electricallyconnected.

.10, A lower operating temperature can be used with a largerpercentageof nickel or cobalt..

For example, if the nickel or cobalt comprises only about five per centof the tungsten carbide,- it may be necessary to use a temperature ashigh 15' .as 2600" 0., in order to melt the entire mass, so

as to recrystallize the tungsten carbide, and to. secure larger crystalsthan in the original tung sten carbide which has been used as thestarting material. The improved material is essentiallyv 20 an alloy,insteadof consisting of cemented particles of tungsten carbide. That is,while parts of the improved material consist of tungsten carbide alone,a'very substantial part of said mate-f rial consists of a true alloy oftungsten carbide 25 or the like, and the nickel or the like. If a largerpercentage of nickel or cobalt is used, such as 25%, it is possible tomelt the mass;

, at about 1800 C., which is higher than. the sintering temperature ofabout 1420 C. The nickel 3. will not melt so as to separate from thetungsten carbide, because the particles of tungsten carbide aresufliciently fine and the coating of nickel or cobalt is suiiicientlyphysically combined with the particles of tungsten carbide.

Likewise, I melt the mass without any'substantial stirring, because theingredients have been premixed and physically combined, so that .L thenickel does not melt so as to separate from the tungsten carbide or thelike. The improved material is of superior strength so that wire-drawingdies'made therefrom have a longer life and can withstand higher burstingstresses. Y 45 Fig. 3 shows how the particles of tungsten carbidematerial or the like can be located within a shell l6, which can be madeof'nickel or cobalt or the like. Said shell may have a bottom wall. Theparticles of tungsten carbide which are 10- o cated within said shellmay be, coated.with a small percentage of nickel -or cobalt, less than5% of the tungsten carbide by weight. For example, the-,percentage ofnickel or cobalt which has been used to coat the particles of tungsten55 carbide, may be as lowas 2%. The metal thimble l6 containing thecoated particles of tungsten carbide or the'like, is placed within themould, and treated in the manner previously specified. The metal thimblemelts, so as to produce a slug 60 or mass which has a varying percentageof nickel or cobalt or the like therein, from the centre of the slug tothe periphery thereof. For example, the central part of said slug ormass may have substantirlly two per cent or nickel or oo- 5 bait, oreven less, and in as small a; percentage as may be desired, dependingupon the amount of nickel or cobalt which has been used initially tocoat the particles of tungsten carbide. At the periphery of said slugand at one end thereof, 7 said mass or slug may have almost one hundredper cent of cobalt or nickel or the like. As the cobalt or nickel ismelted, according to the process previously specified herein, saidcobalt or nickel which results from the melting 'of the 7 thimblepermeates the particles of tungsten duce a slug of less height andvolume particles of tungsten carbide, prior to the use of carbide orother material inwardly from the.pe-

'riphery of the 81118.

If desired, said metal thimble can be replaced by an annular shellhaving no top or bottom. This shell can be located within the mould 5against the interior wall-ofthe mould, andthe particles of tungstencarbide can be placed withinsaidshell. ,1

Hence the total percentage of nickel or cobalt in the entire final denseslug, may be 20% or 10 even higher, and the central part of said slugmay contain 5% or less of nickel or cobalt or the like, and thispercentage may be as low asis desired. Hence, if the slug is used formaking a wire-drawing die which has a fine bore, the wall of said boremayconsist essentially of tungsten carbide-having as little as 5% or 2%or less of nickel or cobalt or the like. As the bore is enlarged, due tothe wearing out of the die and the" reboring thereof, the wall of thebore has an increasingly larger percentage of nickel. This isadvantageous because the material which has a,

very-low percentage oi'nickel or cobalt is extremely hard, and thematerial which has the 'Tests'have shown that the process abovementioned is a true'melting process, because it is not necessary to usepressure in order to melt the coated particles of tungsten carbideand-to proan the original mass of material. The pressure is used merelyto. drive occluded air out ,of the mass, so as to produce a dense masshaving the necessary strength, and to eliminate voids which might beproduced by the presence of air or gases.

Whenever I refer to the coating of the particles of refractory carbide'material or the like with a-metal, I do not wish to be limited to theformation of a complete coatingon said parti- 40 cles, although'I preferto form a complete coating on said particles. v

While I prefer to cause the molten nickel or cobaltor the liketo-permeate a mass of particles of tungsten carbide or the like, fromthe periphery of said mass of particles, I do not wish to be limited tothis, as particles of nickel or cobalt or the like which are larger thanthe particles of tungsten carbide, may be mixed with the said heat. Fig.7 shows the starting material or powder which is utilized for making theimproved material. The grain or crystalsize and formation I are clearlyshown in Fig. 7.

Fig. illustrates the change in the starting materi of Fig. 7 by usingthe method herein stated, but without the use of any pressure. Fig.

5 shows that the structure of the material consists of medium largetungsten carbide'crystals with a very small amount of a matrix, saidmatrix consisting of a solid solution of tungsten carbide cobalt. I

Fig. '5 shows that the tungsten carbide mate- 05 rial has beenrecrystallized. Hence, whenever" I refer to fusing or melting thestarting material illustrated in Fig. '7, I refer to a method wherein'the above mentioned matrix is formed, and the tungsten carbide or thelike has been recrystal- 7 lized.

Fig. 6 illustrates. amaterial which has been made according to thecomplete process above described, using a temperature of 2200 C. to2300" C.

The maximum pressure utilized was 2000 pounds per square inch.

The first step wasto apply a pressure of 500 pounds vper square inch andthen to supply the heating current to the'coil G. 'I'hepressure was thenincreased to 2000pounds per square inch. The original particle size ofthe tungsten carbide powder which was used as a startingmate rial was0.0002 inch (two ten-thousandths 015 an inch). This original startingmaterial had 10% by weight of cobalt. I

Upon analyzing the final material which vre sulted from the use of thisstarting material, it was found that about 12% of the weight of theoriginal starting material had been lost. When the original startingmaterial had 10% by weight of cobalt, analysis showed that the finalmaterial illustrated in Fig. 6 had about 2.62% by weight of cobalt.Since the total loss of the material r was 12% by weight of the originalmass, the madifiers mainly from the material illustrated in Fig. by thecomplete absence of the voids which are shown in Fig. 5.

' Likewise in Fig. 5 nearly all the crystals are of medium size, whereasthe material illustrated in Fig. 6 has crystals of tungsten carbidewhich vary in size from the small size to the medium size.

A comparison between Fig. 5 and Fig. 6 and Fig. 7, shows the differencein the crystals of tungsten carbide, due to the recrystallizationthereof by the method .above specified. In making the materialillustrated in Fig. 6, the time of operation was from seven minutes to 8minutes.

It will be noted that according to the improved method, the refractorymaterial, such as tungsten carbide, is initially physically associatedwith a metal having a lower melting point than said refractory materialand that some of this low-melting metal is eliminated from therefractory material, during the heating operation above specified.

It is believed thatxthe addition of a, relatively large percentage ofcobalt to the initial material, by the method above specified, makes itpossible to lower themelting point of the mixture so that the operatingtemperature need not. exceed 2200 C. to 2300? C.

I can produce a final alloy of the type shown in Fig. 6, and having anydesired percentage of nickel or cobalt or the like, by incorporating a.suificiently large percentage of nickel or cobalt or' thelike into thestarting material.

Likewise the elimination of nickel or cobalt or the like from therefractory material, can be controlled by regulating the workingtemperature, or the time of operation, or the porosity of the graphitemould or the like.

There are certain of graphite which are extremely dense so that theelimination of nickel or cobalt or the like is much less than if thegraphiteisrelatively porous.

Whenever I, refer to an alloy in the claims, it is to be understood thatI intend to cover the material illustrated in Fig. 5 or in Fig. 6, andwhich consists essentially of masses or crystals of the refractorymaterial, held in a matrix which consists of a solid solution of therefractory materiaL and an auxiliary metal having a lower melting pointthan said refractory material.

I do not .wish tobe limited to any particular method of heating thecoatedrefractory particles.

It will be'noted that according tothe preferred method the particles aresubjected to heat and pressure without any substantial stirring action.

'I have shown a preferred embodiment of my invention, .but it is clearthat numerous changes and omissions can .be made without departing fromits spirit.

The graphite plunger 8 may be very dense, so that little or no materialenters it, or said plunger may have the same structure as the graphitemold. I claim:

1. In the art of making an alloy which includes a major proportion of ametallic carbide whose melting point exceeds 2000 C. and a minorproportion of a metal whose melting point is below 2000 C., in anenclosed mold having a movable ram which projects from a wall of saidmold, those steps which consist in heating said metallic carbide andsaid metal in said mold while exerting pressure on the heated materialby moving said ram, while compressing powdered portion of the mold, andthen cooling the heatedand pressed material in said mold.

2. In the art of making an alloy which includes a major proportion of ametallic carbide whose melting point exceeds 2000 C. and a minorproportion of a metal whose melting point is below 2000 0., in anenclosed mold having a movable ram which projects from a wall of saidmold, those steps which consist in heating said metallic carbide andsaid metal in said mold while exerting pressure on the heated materialby moving said ram, while compressing powdered material externallyaround said ram and said mold at said wall of the mold to hinder theentry of air between said ram and the adjacent wall portion of the mold,and then cooling the heated and pressed material in said mold, said-metallic carbide being crystalline, the heating temperature beingsufilciently high to recrystallize said metallic carbide during saidcooling.

3. In the art of making an alloy which includes I a. major proportion ofa metallic carbide whose melting point exceeds 2000" C. and a. minorproportion of a metal whose melting point is below- 2000 C.,' in anenclosed mold having a movable ram which-projects from a wall of saidmold,

those steps which consist in heating said metallic carbide and saidmetal in said mold while exerting pressure on theheated material bymoving said ram, while compressing powdered material externally aroundsaid ram and said mold pressed material in said mold, said metalliccar-' bide and said metal being heated by subjecting them to a. varyingelectro-magnetic flux which induces a secondary voltage having a closedcircuit within said carbide and said metal and the wall of the mold.

4. In the art of making an alloy which includes 1 a major proportion ofa metallic carbide whose melting point exceeds aoocr c. and a minorpro-g portion of a metal whose melting point is below 2000 0., in anenclosed mold having a movable ram which projects from a wall of saidmold. those steps which consistin heating said metallic carbide and saidmetal in said mold while exerting pressure on the heated material bymovture being suiiiciently high to. recrystallize said metallic carbideduring said cooling, said metallic carbide and said metal being heatedby subjecting them to a varying electro-magnetic flux which induces asecondary voltage having a closed circuit within said carbide andsaidmetal,

and the wall of the mold.

5. A method according to claim 1, in which the metal is in the form of acoating on the metallic carbide, and the metallic carbide is in the formof particles whose average diameter does not exceed 0.0002 inch.

' LEON SIMONS.

